The present invention relates generally to a sound reduction control system and method for a cooling system. More specifically, the present invention relates to a system and method for reducing the sound generated by a compressor driven chiller system having a variable speed drive by selectively and controllably reducing the speed of the compressor, the speed of the condenser fans, or the number of operating condenser fans in the system.
In chiller, HVAC or refrigeration systems, a refrigerant gas is compressed by a compressor and passed to a condenser where it exchanges heat with another fluid, such as the ambient air forced over condenser coils by one or more condenser fans. From the condenser, the pressurized refrigerant passes through an expansion device and then to an evaporator. An environment to be cooled is cooled by refrigerant passing through the evaporator. The refrigerant returns from the evaporator back to the compressor, and the cycle is repeated.
Large capacity chiller systems are required to provide adequate cooling of the interiors of large buildings. Such systems typically include one or more compressors, as well as one or more air-cooled condensers having condenser fans for cooling the compressed refrigerant. Compressor speed and condenser fan speed, or number of condenser fans running, are interdependent on one another. When the compressor operates at a higher speed, a higher rate of compressed refrigerant is passed to the condenser. In order to cool the increased flow of compressed refrigerant, a larger rate of heat exchange by the condenser is required. One way to increase condenser heat exchange is to increase airflow across the condenser coils. Accordingly, operation of a higher number of condenser fans, or operation of the fans at a higher speed, will increase airflow around the condenser coils, resulting in higher rate of heat exchange by the condenser.
Increasingly, it is necessary to reduce the total sound generated by chillers during certain times, particularly for chillers installed near residential areas. Indeed, some localities have laws that require sound levels at property lines to be lower at nighttime than during the day. One known method of reducing the chiller noise is to disable the system during selected hours, thereby preventing the generation of noise by the chiller system. However, disabling the chiller system means that no cooling can be performed by the chiller systems, thus causing the interior building temperatures to rise to uncomfortable levels. Therefore, it would be advantageous for a building owner to be able to reduce the sound level of the chiller system at selected times, while maintaining some cooling capability within the building.
The sound generated by a typical air-cooled compressor chiller system is predominately created by the compressor and the condenser fans. Therefore, in order to reduce the amount of sound generated by the chiller system, it is desirable that the compressor and the condenser fan(s) be made to operate more quietly. This goal can be accomplished by several known ways. For example, mechanical modifications such as the application of sound-insulating coatings can be made to the compressor, condenser fans, and any housings encasing such components, to reduce operating noise. Alternatively, new compressors and new condenser fans manufactured with sound-absorbing or sound-attenuating features can be installed. However, such modifications or replacements can be expensive as a result of the materials, labor, and downtime costs that are potentially involved. Therefore, what is needed is a cost-effective method for selectively reducing the noise generated by an installed chiller system.